1. Field of the Invention
The present invention relates to a recording technique wherein an image is formed by supplying toner between a recording medium and a recording electrode which are disposed to be spaced apart from each other, and more particularly, it relates to a large-sized recording electrode used with such recording technique.
2. Related Background Art
An image forming process wherein a developer (toner) is adhered to a recording medium by using a recording electrode is already known as disclosed in the Japanese Patent Publication No. 51-46707 (U.S. Pat. No. 3,914,771) and the like. In this image forming process, as shown in FIG. 4, electroconductive and magnetic toner (referred to as merely "toner" hereinafter) 1 having a resistance of 10.sup.3 -10.sup.9 .OMEGA..multidot.cm is conveyed on a non-magnetic cylinder 3 made of stainless steel, aluminum or the like by means of a rotary magnet 2 to pass through a recording electrode 4 made of conductive material such as metal. A voltage is applied between a conductive layer 7 of a recording medium 5 including an insulation layer 6 having a thickness of 1-20 .mu.m and a resistance of 10.sup.7 -10.sup.16 .OMEGA..multidot.cm and the recording electrode 4, whereby the toner is adhered to the recording medium 5, thus forming the image.
FIG. 5 shows, in section, a whole construction of a display device using such image forming process.
In FIG. 5, the reference numeral 1 denotes the toner; 4 denotes the recording electrode; 5 denotes a recording medium comprising an endless belt (referred to as "recording belt" hereinafter); 8 denotes an erasing member utilizing a sliding friction function; 10 denotes a toner container; 11 denotes support rollers for supporting the recording belt 5; 12 denotes a body frame having an optical displaying opening 25 formed therein; and 13 denotes a recording control portion. Prior arts regarding such display device are disclosed or described in U.S. Pat. Nos. 4,739,348 and 4,788,564 and U.S. Ser. No. 401,243 (filed on Aug. 31, 1989 in USA), now U.S. Pat. No. 5,001,501).
With this arrangement, the image is formed by the fact that the toner is adhered or not adhered to the recording belt 5 in response to a signal voltage from the recording electrode 4. For example, when the signal voltage of 40 V is applied from the recording control portion 13, the toner 1 is electrically adhered to the recording belt 5, whereas, when no signal voltage is applied, the toner is not adhered to the recording belt due to the attracting force of the magnet 2, thus forming the image on the recording medium. After the toner image is formed, by rotating the recording belt supporting roller 11 by means of a motor (not shown), the recording belt 5 is conveyed in a direction shown by the arrow. After the image is displayed, the toner 1 is electrostatically removed and mechanically stripped from the recording belt 5 by the erasing member 8 made of conductive carbon fibers, conductive resin or conductive rubber. The toner 1 is dropped onto the toner container 10 by its own weight, thus preparing for the next recording operation.
FIG. 6 is a schematic front view of the recording electrode 4 used with such image recording system.
An electrode member constituting the recording electrode 4 is constituted by conductive portions 4a of the electrode made of copper and the like and insulating portions 4b made of polyamide and the like which are disposed on a flexible print substrate 4c by an etching treatment. Further, on the flexible print substrate 4c, there are arranged IC elements (not shown) for activating the conductive portions 4a, IC elements (not shown) for latching image information inputted from an external equipment, connectors (not shown) connecting to cables for inputting the image signal, power source and recording power source, and the like.
FIG. 7 shows the conductive portions 4a and the insulating portions 4b of the recording electrode in an enlarged scale, wherein a distance between the adjacent conductive portions 4a (internal of the insulating portions) is 0.26 mm and a distance between the adjacent insulating portions 4b (width of the conductive portion) is 0.11 mm. In the recording process used in this conventional example, although it is desirable that the interval of the insulating portions 4b is smaller as much as possible, due to the limitation of the etching treatment technique, when a thickness of a copper foil constituting the conductive portion 4a is 16 .mu.m, the width of the insulating portion is limited to about 0.1 mm at the minimum. If the insulating portion 4b having a width less than 0.1 mm is used, the adjacent conductive portions 4a are short-circuited with each other, thus giving rise to a problem that each conductive portion cannot be independent from other conductive portions. Further, the width of each conductive portion 4a is determined by the number of pixels for the image and normally, 1680 pixels are included in the width of the conductive portion. In this case, a width of the recording electrode becomes: EQU 1680.times.(0.26 mm+0.11 mm)=621.6 mm.
Further, recently, a large-sized display device has been wanted or required, and accordingly, the above-mentioned width of the recording electrode cannot meet such requirement. For example, although the recording electrode having a width of 1.5 m has been required, since the normal flexible print plate constituting a base of the recording electrode has merely a dimension of 800 mm.times.800 mm, it was impossible to manufacture the recording electrode having the width of 1.5 m in one piece. Thus, in the past, two recording electrodes each having a width of 750 mm were manufactured and these electrodes were arranged side by side and connected by adhering the end insulating portions thereof to each other, thus obtaining the recording electrode having the width of 1500 mm.
FIG. 8 shows the recording electrode having the width of 1500 mm schematically FIG. 9 shows, in section, a connecting portion between two recording electrodes, and FIG. 10 shows the connecting portion as a plan view. In this connecting portion, since the insulating portions 4b of two recording electrodes are adhered to each other, as apparent from these Figures, the width of the insulating portion across the connecting portion is not 0.11 mm.
The images formed by using the recording electrode shown in FIGS. 8 to 12 are shown in FIGS. 11 and 12.
FIG. 11A shows an all black image (having no white area therein). However, in the conventional technique, since the pitch between the conductive portions in the connecting portion is wider, a problem that a white stripe is generated occurs, as shown in FIG. 11B. On the other hand, FIG. 12 shows an image comprising white and black stripes alternately. However, in the conventional technique, as shown in FIG. 12B, there arises a problem that the width or pitch of the white stripe in the connecting portion is wider and a ghost is generated in this white stripe. The reason is that the toner is clogged in the connecting portion and this toner is adhered to a recording sheet. Incidentally, a condition that the toner is clogged in the connecting portion is shown in FIG. 9.